Patients with ventricular tachyarrhythmias exhibit a number of abnormalities that must coexist in order for the arrhythmia to become manifest. The "late potentials" detected by the signal averaged electrocardiogram represent the substrate for reentrant type ventricular arrhythmias. Given the appropriate substrate, changes in autonomic tone may serve as the triggers for inititation of ventricular arrhythmias. To date, no studies have systematically examined the effects of autonomic activity on "late potenitals." Our preliminary data show that B- adrenergic stimulation with epinephrine infusion prolongs the QRS duration, presumably related to conduction slowing. Because myocardial infarction may lead to autonomic denervation in the surviving myocardium adjacent to the infarction, resulting in supersensitivity of this tissue to catecholamines, B-adrenergic stimulation with epinephrine might be expected to have a more pronounced effect on late potentials which arise from this area. Our data also suggest that the end diastolic volume affects the QRS duration. This protocol is designed to comprehensively evaluate a variety of factors (autonomic tone, left ventricular end diastolic volume and systolic function, heart rate, serum potassium, and blood pressure) that may affect the signal averaged electrocardiogram and late potentials.